Suppose that 20 pillars of the same height have been erected along the boundary of a circular stadium. If the top of each pillar has been connected by beams with the top of all its non-adjacent pillars,then the total number of beams is :

Suppose that 20 pillars of the same height have been erected along the boundary of a circular stadium. If the top of each pillar has been connected by beams with the top of all its non-adjacent pillars,then the total number of beams is :

  1. A

    170

  2. B

    190

  3. C

    180

  4. D

    210

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    Solution:

    Since, 20 pillars are connected by beams with all  its non adjacent pillars.

     Total number of beams =20C220

    =20!18!2!20=20×19220=170

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